After wheat and canola, barley is the most prominent crop in Western Canada. From 2005 to 2014, an average of 7.9 million acres was seeded resulting in an average annual production of 9.2 million metric tonnes. Barley grain has two primary end uses: as malt for beer or as livestock feed. On average, the value of malt barley is 60 per cent higher than feed barley. In Canada, more than 50 per cent of the barley seeded is grown for malt and as a result most breeding programs focus on improving brewing traits. However, barley must meet a rigorous set of criteria to qualify as malt. Of these traits, the most important are hot water extract, viscosity, Kolbach Index, wort ß-glucan, fermentability and diastatic power (DP). Barley that fails to make malt (75 per cent to 80 per cent of production) is relegated to feed. As a result, barley is the most common grain fed to feedlot cattle in Western Canada.
Feed barley is marketed mainly by bushel weight, degree of plumpness, and percentage of thins, traits that show only a modest relationship to its feed value for ruminants. Recently, we undertook a project to access the relationship between the malt and feed value of barley grain, and identified diastatic power as a malt trait that is negatively correlated with the digestion of barley (at least barley incubated in nylon bags in the rumen for four or 12 hours). Thus, lower diastatic barley would be more digestible in the rumen and have higher feed value.
Diastatic power reflects the combined activities of four enzymes (alpha-amylase, beta-amylase, limit dextrinase, and alpha-glucosidase that solubilize starch to fermentable sugars during malting. Of these enzymes, beta-amylase is the only one that is normally active in barley; the remainder become active during germination.
Thus, low-diastatic power barley is undesirable for malt as it indicates that the level of starch-degrading enzymes in the barley will be too low to produce the sugars that are fermented to alcohol during beer production.
Diastatic power in barley is influenced by genetic and environmental factors and is predicted using near-infrared spectroscopy (NIRS) when assessing malt quality.
If diastatic power also has a relationship to barley’s feed value, an index of feed quality could be generated at the same time as the barley is assessed for malting quality.
Barley that differs in diastatic power may also respond differently to processing methods such as dry- or temper-rolling. Processing of barley grain is necessary to disrupt the fibrous hull and pericarp so rumen bacteria can access the starch in the endosperm and release the sugars required for ruminal fermentation. However, excessive processing may cause the sugars to be released too quickly, leading to acidosis and compromising the growth performance and carcass quality of feedlot cattle.
The degree of processing of barley grain is often assessed by measuring the processing index (PI), which is calculated by dividing the weight of the grain after processing by the weight before processing and multiplying by 100.
Grain with a lower PI is more extensively processed.
We conducted a study using feedlot steers to evaluate the feed value of high- and low-diastatic power barley grain that was dry-rolled at a low (75) and high (85) PI.
We observed that low-diastatic power barley consistently had a higher starch and lower protein content. Consequently, measuring diastatic power during malt grading can also be used to predict the protein and starch content of barley.
Lower rumen pH was also observed just prior to feeding in steers fed low-diastatic barley as compared to high-diastatic barley.
Feed intake was not affected by diastatic power, but was lower with more severe grain processing (PI-75 versus PI-85).
Low-diastatic power barley tended to be more digestible than high-diastatic power barley, likely because of its higher starch content. Steers fed more highly processed (PI-75) barley also had higher gain:feed and net energy for gain (NEg) values.
Digestibility was also higher for PI-75 barley as compared to PI-85 barley.
Low-diastatic power barley combined with a lower processing index increased carcass dressing percentage by 0.5 per cent, tending to also increase ribeye area. Compared to high-diastatic power barley, steers fed low-diastatic power barley diets had more total (41.7 per cent versus 19.4 per cent) and severe liver abscesses (22.2 per cent versus 9.7 per cent), a finding that may be linked to lower rumen pH.
These results suggest that while low-diastatic barley increased liver abscesses, it did not alter digestion or growth performance, but did improve dressing percentage. Barley differing in diastatic power responded the same to processing. More intensive processing improved starch digestion, feed efficiency and net energy for gain.
This suggests when barley fails to meet the malt grade producers could use the diastatic power reading as an immediate indicator of the barley’s feed value.
Calibration equations that predict diastatic power using near-infrared spectroscopy (NIRS) are available and could be used by feedlot producers that possess NIRS machines to predict the feed value of any barley.
This study also shows that grain processing has a greater impact on feedlot cattle performance than any slight differences in the composition of barley grain. Thus, feedlots should pay close attention to the processing of barley grain if they are to derive the greatest feed value from barley.
Gabriel Ribeiro is a visiting scientist and Tim McAllister is a principal researcher with Agriculture and Agri-Food Canada at the Lethbridge Research Centre, where they study various aspects of feedlot cattle production.